The present invention relates generally to semiconductor memories, and more particularly to a serial electrically erasable programmable read only memory (EEPROM) for use in applications requiting storage and serial transmission of configuration and control information.
There is often a need to configure and reconfigure an intelligent peripheral device such as a monitor or a scanner to operate in different modes which are selected according to the needs of the apparatus with which the peripheral is operated. Since the advent of personal computers (PCs), for example, means have been available by which to run a program utilizing the PC monitor to provide a desired display mode. The monitor could be commanded to operate in one particular mode of the plural modes available for operation. Upon receipt of such a command, the video controller card responded by switching to the designated display mode, and the monitor automatically assumed that mode. Although no communication path existed by which the mode would be switched, the PC recognized that the video controller card had changed the scan rate, and responded with the mode switch. The monitor change was accompanied by an audible click attributable to relays changing the display mode.
It would be desirable to accommodate any of a plurality of possible modes by configuring an intelligent peripheral device automatically, without need for anything other than a recognition of the mode of a related device, and, indeed, by simply responding at the time of power-on of the peripheral device.
In 1993, the Video Electronics Standards Association (VESA) announced a proposed standard which defines a communication channel between a computer display and a host system for carrying configuration information to optimize use of the display as well as to carry additional display control information. This so-called display data channel would allow the display to inform the host system about its identity, and, depending on which of two types of the channel was used, viz., a uni-directional type and a bi-directional type, would allow the display to communicate additional levels of display capabilities.
It was deemed that this scheme represented a departure from earlier monitor identification (ID) schemes which only allowed for ID of a limited number of displays and display parameters, and carded no information about capabilities of the display. Consequently, it was felt that such earlier schemes had little use when connecting a new display to an existing host. An important objective of the VESA-proposed data display channel was to provide information for automatic configuration of a display controller based on the capabilities of the display.
Of the two data channel types, the uni-directional type is to provide a data channel from the display to the host to continuously transmit an ID data structure containing display identity and basic display specifications information. The other, a bi-directional type is based on the inter integrated circuit (I.sup.2 C, which is a trademark of N.V. Philips Corporation of the Netherlands) protocol. In the latter type, the host may request extended data ID or a data structure containing full display specifications.
In U.S. Pat. No. 5,276,458 to Sawdon, assigned to International Business Machines (IBM) Corp., a VESA member, a computer system has a display device for displaying visual information, and a display adapter for processing the information to be displayed on the display device. The display adapter includes a device driver that responds to a program instruction to transmit a command bit stream to the display device. A decoder decodes a response bit stream transmitted from the display device upon receipt of the command bit stream, to generate data and control signals compatible with a display mode of the display device.
It would desirable to have the availability of a stand-alone memory device with the capability to provide automatic switching of data stream transmission modes for a multiplicity of applications involving intelligent peripheral devices and a host computer or other data processor.
It is a principal object of the present invention to provide such a stand-alone memory device.
It would also be desirable to provide such a memory which is I.sup.2 C bus-compatible for two wire serial interface bus operation. The I.sup.2 C bus developed by Philips takes advantage of the similarity between designs of systems component devices from different sources, to allow communication and control functions between circuit chips, or ICs, constituting the different component devices. In essence, an I.sup.2 C bus-compatible (or simply, I.sup.2 C-compatible) device incorporates an on-chip interface for communication directly with other such devices by means of an I.sup.2 C bus, to avoid interfacing problems between chips of otherwise unrelated or only slightly related designs.
The I.sup.2 C bus has two bus lines, one being a serial data (or SDA) line, and the other a serial clock (or SCL) line. Devices connected to the bus are software addressable and have master/slave relationships with other I.sup.2 C compatible devices connected to the bus. The bus employs features such as collision detection and arbitration to prevent data corruption when two or more masters are vying for bus access, and allows serial, 8-bit oriented bi-directional data transfers at moderate speeds. The features and capabilities of the I.sup.2 C bus are such that system designers are able to bring their designs rapidly to prototype stage, and to implement modifications as desired, by the technique of clipping or unclipping I.sup.2 C-compatible chips vis-a-vis the bus.
Accordingly, a memory device which is capable of automatic switching of data stream transmission modes for a multiplicity of intelligent peripheral applications, and which is also I.sup.2 C-compatible, is a powerful device for the systems designer, and for actual systems use.
It is therefore another important object of the present invention to provide a memory device having the capability of automatic switching of data stream transmission modes, as well as I.sup.2 C compatibility.